The present invention relates generally to an electronic apparatus, and more particularly to methods for providing physical connection of semiconductor devices to circuit boards without using a surface mounting process.
Circuit board manufacturers/assemblers have to physically attach a variety of semiconductor devices to their board to produce their end product. A common method for attaching semiconductor devices to the circuit boards is to place the semiconductor devices in the appropriate positions on the board, and to subject the board to a high temperature reflow operation. In the reflow operation, a connection medium, such as solder, is used to mechanically and electrically bond the external terminals of the semiconductor device to the appropriate landing pads on the circuit board.
Often times, a circuit board assembler does not use the same semiconductor components on all boards that are being assembled. For example, a manufacturer who is assembling boards for use in a computer may want to attach varying numbers of semiconductor memory devices, such as fast static random access memory (SRAM) devices. Rather than subjecting one set of boards to a reflow operation having the SRAM devices and subjecting another set of boards to a reflow operation without fast static rams, it is desirable for a larger set of identical boards to be subjected to the reflow operation, with optional components, such as additional memory, being added to the board just prior to shipment to the customer. Such a system would simplify the assembly process. Moreover, it would be attractive if the optional devices could be attached to the circuit board without an additional reflow operation. In particular, it would be desirable if the optional devices to be attached to the board could be connected without forming a thermally-induced metallurgical connector between external terminals of the device and the conductive pads on the circuit board. The process of forming the metallurgical bonds (i.e. the reflow or surface mount process) is time consuming, adds excessive manufacturing costs, and precludes easy removal or replacement of the optional devices so attached.
While a variety of non-metallurgical mechanical connections have been proposed in the prior art, known mechanical connections have several disadvantages. For example, it is known to use a rigid plate in combination with bolts and nuts to hold a semiconductor device against a printed circuit board. However, a disadvantage of this process is the number of piece parts which are required in the assembly of such circuit boards, and the difficulty in getting a uniform force across the plate due to variations in torque between the various nuts. Another method of providing mechanical connection of a semiconductor device to a circuit board is through the use of a hinged socket. The socket is connected to the circuit board, and the semiconductor device is placed in between the two hinged members of the socket. The socket is then closed and an electrical connection is made between the semiconductor device and the circuit board through spring-loaded conductive members. A disadvantage with the use of a socket, however, is that the sockets are expensive, primarily due to the need for spring-load conductive members, and undesirably increase the profile or height of the final circuit board assembly.
Accordingly, a need exists for an improved method for electrically connecting a semiconductor device to a circuit board after the board has undergone a traditional reflow operation. More particularly, a need exists for providing electrical connection between a device and a circuit board without forming thermally-induced metallurgical connections between the device and the circuit board. Moreover, it would be desirable for such a method to be inexpensive in material costs, to provide minimal height to the final circuit board apparatus, and to be easy to manufacture and assemble with a minimal number of piece parts.